Chromosome Manipulations in Alfalfa: Scaling the Cultivated Tetraploid to Seven Ploidy Levels1

The general scheme used in scaling genomic multiples down and up in ploidy is summarized, and a specific case of scaling chromosomes of a single cultivated alfalfa (Medicago sativa L.) clone to seven ploidy levels is reported. Cultivated tetraploids were scaled down to the diploid level by haploidy. Scaling upward was accomplished by sexual polyploidization, colchicine chromosome doubling, and spontaneous doubling in tissue cultures. The resulting ploidy series is diploid, triploid, tetraploid, pentaploid, hexaploid, heptaploid, and octoploid. For the single clone, this is the greatest range in ploidy levels known to have been produced with the chromosomes of a single individual. It demonstrates the plasticity of the autopolyploid genome of alfalfa and its ability to function at extremes of polyploidy. It further demonstrates how gene flow can be accomplished in a polyploid series through interploid crosses and bridge crosses. Such gene flow may prevent autopolyploids from becoming dead ends in evolution and isolated in breeding programs. Data on seed size at 2x, 4x, and 8x levels are also reported.